1. Field of the Invention
The present invention relates to a light emitting diode (LED) illumination device and method and more specifically to a light emitting diode, integrated with electronic circuitry.
2. Description of Related Art
Currently lighting applications are dominated by incandescent lighting products. Because they use hot filaments, these products produce considerable heat, which is wasted, in addition to visible light that is desired. Halogen based lighting enables filaments to operate at a higher temperature without premature failure, but again considerable non-visible infrared light is emitted that must be disposed of. This is conventionally done by using a dichroic reflector shade that preferentially passes the infrared as well as a portion of the visible light. The nature of this dichroic reflector is such that it passes several different visible colors as well as the infrared radiation, giving a somewhat pleasing appearance. This has lead to numerous applications for the halogen lights in which the entire light is used for decorative purposes. These lights consume substantial current and dissipate considerable unwanted heat. These bulbs are designed to operate at a variety of voltages between 12 Volts to as high 115 Volts or greater.
Light emitting diodes have operating advantages compared to ordinary incandescent as well as halogen lights. LEDs can emit in a narrow range of wavelengths so that their entire radiant energy is comprised within a predetermined range of wavelengths, eliminating, to a large degree, wasted energy. By combining light colors white can be created. Because such LEDs can now emit in the ultraviolet, the emitted radiation can also be used to excite a phosphor to create white light and other hues.
LEDs have an extremely long life compared to incandescent and halogen bulbs. Whereas incandescent and halogen bulbs may have a life expectancy of 2000 hours before the filament fails, LEDs may last as long as 100,000 hours, and 5,000 hours is fairly typical. Moreover, unlike incandescent and halogen bulbs, LEDs are not shock-sensitive and can withstand large forces without failure, while the hot filament of an incandescent or halogen bulb is prone to rupture.
Halogen bulbs, incandescent bulbs, and LEDs all require a fixed operating voltage and current for optimal performance. Too high an operating voltage causes premature failure, while too low an operating voltage or current reduces light output. Also, the color of incandescent and halogen lights shifts toward the red end of the visible spectrum as current and voltage are reduced. This is in contrast to LEDs, in which only the intensity of the light is reduced. Furthermore, as the voltage to an incandescent and halogen light is reduced, its temperature drops, and so its internal resistance decreases, leading to higher current consumption, but without commensurate light output. In cases where batteries are used as the source of energy, they can be drained without producing visible light.
Incandescent and halogen bulbs require a substantial volume of space to contain the vacuum required to prevent air from destroying the filament and to keep the glass or silica envelope from overheating and to insulate nearby objects from the damaging heat. In contrast, LEDs, being solid state devices, require much less space and generate much less heat. If the volume of an incandescent or halogen bulb is allocated to a solid state LED light, considerably more functions can be incorporated into the lighting product.
Unlike incandescent and halogen lights, LEDs ordinarily produce light in a narrow, well defined beam. While this is desirable for many applications, the broad area illumination afforded by incandescent and halogen lights are also often preferred. This is not easily accomplished using LEDs. The light produced by incandescent and halogen lights that is not directed towards the target performs a useful function by providing ancillary illumination and a decorative function. Halogen lights with their dichroic reflectors do this unintentionally, but ordinary incandescent lights employ external shades, not part of the light bulb, in a variety of artistic designs to make use of this otherwise misdirected light.
LEDs are advantageous in that they consume far less electrical power than incandescent lights, on the order of one-sixth as much power, for a given light output. However, LEDs are subject to thermal damage or destruction at temperatures that are much lower than those tolerated by incandescent bulbs. LEDs are damaged at temperatures exceeding about 150 degrees Centigrade (423° K). This is in contrast to typical incandescent bulbs that typically operate at 3000 to 6000° K.
Additionally, incandescent bulbs are self regulating by increasing the internal resistance of the bulb as power to the bulb is increased. This limits the amount of current that flows through the bulb and maintains the bulb within an operating temperature range that is non-destructive. On the other hand, LEDs are subject to a thermal runaway condition in which excessive power causes the LED to heat and lower the LED internal resistance, which causes more current to flow and more heating to occur. This thermal runaway can cause the operating life of the LED to be severely shortened or may lead to the rapid destruction of the LED.
LEDs can only operate over a relatively narrow operating voltage, typically from about 2 to 4 Volts. Most power sources provide a voltage that is not in the range needed to safely drive the LEDs. Because of this, voltage regulation is required to convert the range of available line voltages, and in some instances battery voltages, into levels that are useful for powering the LEDs.
Voltage regulation is accomplished using electronic circuitry, such as surface mounted electrical components that are mounted to a printed circuit board (PCB). These electrical components can be installed on the PCB along with the LEDs. PCBs are usually made of alternating layers of insulating materials such as fiberglass and copper foil for forming complex circuits. These types of PCBs typically do not efficiently conduct the heat generated by the electrical components and LEDs away from the LEDs. Metal core boards made with aluminum are more efficient at conducting heat away from the LEDs, however these boards are much more expensive and are limited to a single side to contain circuitry. Typical metal core boards and fiberglass/copper PCBs used for high density LED light applications do not have sufficient heat conducting capacities to dissipate more than about 1 Watt away from LEDs. Failure to control the heat at the LEDs can lead to the thermal runaway and subsequent damage of the LEDs.
Dimming LEDs, cold cathode fluorescents and other non-incandescent lighting traditionally involves complex circuits using microprocessors. Most conventional incandescent dimmer controls affect the dimming function by reducing line voltage supplied to the fixture. LED and CFL circuits typically contain regulating circuits to convert incoming line voltage power, typically 110VAC in the United States, to a voltage/current that is suitable for the LED or CFL. Modulating the line voltage with a conventional dimming circuit does not produce the desired dimming effect on LED and CFL lighting because of the regulating circuits.
One traditional approach to produce dimming capabilities with conventional dimmer switches is to use a microprocessor and analog-to-digital converter (ADC) to sense incoming voltage and to control the regulated circuit such that the perceived result is equivalent to the dimming of a conventional incandescent bulb. In these circuits, the ADC allows the processor to read the incoming voltage, and the processor then produces a pulse wave modulated (PWM) waveform that modulates a control or sensing signal to the power regulator to reduce the resulting brightness responsive to the modulation. Many power ICs designed for lighting applications provide “dimming” control pins specifically for the purpose of allowing for digital control of the brightness in regulators based on those ICs.
It is submitted that microprocessor based dimming controllers add unnecessary expense and complexity to LED lighting systems. The microprocessors are also subject to heat from the LEDs which can affect the reliability of the circuits.